Indefinite Pronouns

Let's pretend that you want to make a cake. Unfortunately, you haven't got all the ingredients.

There's an orange, some/a lot of flour and some/a lot of milk, but there isn't much/any sugar and there aren't many/any eggs.

The underlined words are indefinite pronouns. We use them with countable nouns (a/an, (a) few, many), uncountable nouns ((a) little, much) or both (a lot of, some, any) when we don't know the exact number or quantity of something. 

Although we've said before that we use SOME in affirmative sentences and ANY in questions and negative sentences, there's an exception to the rule:

Would you like some biscuits? (offer, we expect a positive answer)

Can I have some juice? (request, we expect a positive answer)

One more thing, we use A LOT OF in positive sentences and MUCH/MANY in questions and negative sentences.